1. Field of the Invention
The present invention relates generally to biodegrading contaminated soils and, in particular, to a method and apparatus for the removal of volatile hydrocarbons and the like from contaminated soils.
2. Description of the Prior Art
Recent environmental legislation such as the Comprehensive Environmental Response, Compensation and Liability Act of 1980 and the Superfund Amendments and Reauthorization Act of 1986 have identified certain hazardous waste sites as requiring cleanup utilizing treatment technologies that will permanently and significantly reduce the volume, toxicity, or mobility of hazardous substances at these waste sites. This legislation further directs that permanent remedies be chosen for the cleanup of these hazardous waste sites and that offsite disposal of contaminants should be the least favored alternative for disposal of hazardous waste.
In complying with this environmental legislation the military has identified a significant number of their facilities as being hazardous waste sites requiring cleanup. Typically, the soils at these sites are contaminated with highly volatile hydrocarbon compounds such as gasolines and chlorinated solvents as well as hydrocarbon compounds having moderate to low volatility such as jet fuel, diesel fuel, engine oil and lubricants.
These hazardous waste sites also have underground storage tanks which are regulated by this environmental legislation and which are being used to store diesel fuel, gasoline and jet fuels. A significant portion of these underground storage tanks are over twenty years old or are fabricated from concrete which is permeable to most organic liquids. Thus, there is a high probability, with some estimates exceeding fifty percent, that these underground storage tanks are leaking and thus contaminating the soils surrounding the underground storage tanks.
Biodegradation has long been recognized as a process for the removal of toxic chemicals from the environment. In the past, for example, wastewater treatment plants have used biological processes to remove toxic chemicals and other contaminants from wastewater.
Bioremediation, which is the controlled use of biodegradation to remove toxic contaminants from soil, water and the like has also been used to remove petroleum hydrocarbons from contaminated surface soils and water. Bioremediation generally relies on the hydrocarbon degrading abilities of biological materials such as bacteria, fungi, bacterial enzymes, or fungal enzymes to degrade hydrocarbon contaminated soil. The hydrocarbon degrading biological materials are often naturally present in contaminated soil and given sufficient time can naturally degrade the hydrocarbon contaminants. In addition, this natural degradation process can often be promoted by directly adding biological materials such as hydrocarbon degrading microorganisms to soil in an amount sufficient to degrade the hydrocarbon contaminants or by encouraging the proliferation of hydrocarbon degrading organisms either naturally present in soil or present as a result of inoculation.
Bioremediation of hydrocarbon contaminated soils is favored over soil removal or chemical treatment of soil because of lower cost, proven effectiveness and ability for reduction of hydrocarbon contamination. While satisfactory for their intended purpose of removing contaminants such as hydrocarbons from soil, prior art bioremediation processes ordinarily leave something to be desired in that even under optimum conditions, months or years may be required to decrease the levels of hydrocarbon contamination to the desired levels. This disadvantage has greatly limited the potential use of bioremediation to reduce hydrocarbon contamination in soils.
It is therefore an object of this invention to provide an apparatus and method for accelerated biodegradation of hazardous organic substances in soils.
It is a further object of the present invention to significantly reduce the levels of hydrocarbon contamination of soils within a relatively short period of time after arrival at the hazardous substance contaminated site.
It is yet a further object of the present invention to provide a method and apparatus which permits continual, effective and highly efficient treatment of hydrocarbon contaminated soils.
Various other objects and advantages of the present invention will become more apparent to those skilled in the art as a more detailed description of the invention is set forth below.